This application claims priority to Japanese Patent Application H11-308103 and H11-308104, both filed Oct. 29, 1999.
1. Field of the Invention
The present invention relates to an apparatus and a method for conditioning a polishing pad in a polishing system.
2. Background of the Related Art
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to increase device density on a semiconductor workpiece, or substrate, such as a wafer. As the demand for planarization of layers formed on wafers in semiconductor fabrication increases, the requirement for greater system (i.e., process tool) throughput with less wafer damage and enhanced wafer planarization has also increased.
In an exemplary CMP system, a planarization system is supplied wafers from cassettes located in an adjacent liquid filled bath. A transfer mechanism, or robot, facilitates the transfer of the wafers from the bath to a transfer station. The transfer station generally contains a load cup that positions wafers into one of four processing heads mounted to a carousel. The carousel moves each processing head sequentially over the load cup to receive a wafer. As the processing heads are loaded, the carousel moves the processing heads and wafers through the planarization stations for polishing. The wafers are planarized by moving the wafer relative to a polishing material in the presence of a slurry or other polishing fluid medium. The polishing material may include an abrasive surface. The slurry typically contains both chemicals and abrasives that aid in the removal of material from the wafer. After completion of the planarization process, the wafer is returned back through the transfer station to the proper cassette located in the bath.
Conventional polishing material is generally comprised of a foamed polymer, such as polyurethane, having a textured, grooved, or porous surface. The textured or porous surface functions to retain the polishing fluid that normally contains abrasive slurry on the polishing pad during the polishing operation. The abrasives in the slurry provide the mechanical component of the planarization process which planarizes (i.e., polishes) the substrate in concert with chemical agents present in the polishing fluid.
Both conventional and fixed abrasive polishing materials are generally available in stick-down pads or in the form of a web. Generally, the web is periodically advanced over the course of polishing a number of substrates as the polishing surface of the web is consumed by the polishing process. Conventional polishing materials generally wear during polishing, causing the surface of the polishing material to loose its ability to adequately retain polishing fluid during the polishing process. The resulting non-uniformity of polishing fluid across the conventional polishing material consequently results in variation of the polishing results.
To maintain uniform polishing results, the conventional stick-down pads and webs of polishing material are periodically conditioned by a conditioning disk to return the polishing surface to a condition wherein consistent polishing results can be obtained. Typically, the conditioning disk is covered over its entire bottom surface with a diamond coating. The conditioning disk is rotated so that the bottom surface contacts the polishing surface of the polishing pad. The conditioning disk is connected to an arm so that conditioning disk may be moved to contact the entire polishing surface of the polishing pad.
In the case of fixed abrasive polishing materials, the polishing material is initially conditioned to remove a layer of resin generally disposed at the surface of the polishing material to expose some of the abrasive particles disposed therein. Fixed abrasive webs are incrementally indexed across the area where polishing is performed to remove portions of the web that may have become worn, replacing those portions with an unused portion of the web. Each time an unused portion of web is indexed to the polishing area, that portion of the web must be conditioned to expose the abrasive particles and transform the web to a state where polishing in the unused portion of the web is substantially uniform to the other portions of the web within the polishing area.
A concern during conditioning is particulate generation. Particles formed from either the pad or conditioner may be left on the pad after conditioning. Any individual particle may later scratch the substrates during polishing, creating a potential defect in the substrate or contributing to polishing non-uniformity. For example, a particle disposed on the polishing material may create a high spot that locally concentrates the forces between the polishing material and the substrate. This high force concentration can cause the particle to scratch the substrate. If large numbers of particles are present on the polishing material, local disparities in polishing rates may result in polishing non-uniformities. Moreover, when using fixed abrasive polishing materials, the high force concentration is aggravated by the lower surface contact area between the polishing material and the substrate (about 18 percent for some fixed abrasive materials). This may create excessive shear forces over the particle which may shear the abrasive elements underlying the particle, damaging the polishing material and thus causing scratching.
Therefore, there is a need for an improved apparatus and method for conditioning a polishing pad.
The present invention generally provides an apparatus and a method for conditioning a polishing pad in a polishing system. In one embodiment, the apparatus includes a conditioning disk having conditioning elements disposed on the bottom surface and away from the center portion of the disk. In another embodiment, the apparatus includes a base plate and a ring-shaped plate in which the conditioning elements are disposed on the ring-shaped plate. In still another embodiment, the apparatus includes a conditioning disk having conditioning elements disposed on the bottom surface and away from the center portion of the disk and having brush bristles disposed on the center portion of the disk.